This invention relates to methods for shifting twin-clutch transmissions having two transmission input shafts and a transmission output shaft, each input shaft having a friction clutch on which initially one of the two clutches transmits an engine torque in a state of static friction and the other clutch is open, the gear selected as the new transmission gear after shifting being on the same transmission input shaft as the original gear.
The invention also relates to a twin-clutch transmission having two transmission input shafts and a transmission output shaft for operation in accordance with a gear-shifting method of the invention.
This application is directed to a modification of the shifting method and transmission arrangement described in the application Ser. No. 08/901,917 filed Jul. 28, 1997, the disclosure of which is incorporated herein by reference. That application is referred to herein as the related application.
In the related application, a method is described for shifting a twin-clutch transmission in which, as an alternative, a first clutch of the two clutches is regulated during the gear-shifting operation in such a way that it is in a state of sliding friction. By appropriate control of the remaining, second clutch, it is possible to assure that the first clutch, for the originally engaged gear, is rendered free from transmitted torque by transferring the engine torque to the second clutch, thus making it possible to disengage the original gear.
It is a well-known disadvantage of twin-clutch transmissions having two transmission shafts, which are generally arranged coaxially with respect to each other, that a gear change which covers two gear stages is not possible directly but can only be effected through a gear situated between the two gears under consideration. Twin-clutch transmissions developed hitherto are generally arranged in such a way that the driving gear wheels of respective adjacent gears are situated on different transmission input shafts. Thus, for example, in the case of a six-speed transmission, the odd-numbered gears are on the first transmission input shaft and the driving gear wheels of the even-numbered gears are on the second transmission input shaft.
With such a transmission and with the gear-change method described in the related application, a driver must therefore shift up or down through the gears in numerical sequence. This is a nuisance, particularly during overtaking when, for example, a driver would like to shift down from fourth gear to second gear in order to produce an increased driving power appropriate to the-traffic situation.
It is, however, an advantage of the gear-shifting method described in the related application that the entire drive train is never without torque during gear changing, so that the entire backlash of the individual components in the drive train, which is cumulative, is always held under stress. From this it follows that banging or other torque jumps, which represent severe discomfort for the vehicle occupants, subjectively speaking, cannot occur.
A further major advantage of the twin-clutch transmission and of the gear-shifting method described in the related application is that interruptions in driving power as known from conventional manual transmissions do not occur during gear shifting.